Parallel-slide gate valves essentially consist of a slide gate housing which can be bolted between the pipe end flanges and a plane parallel slide gate plate which can be adjusted to an open, a closed or an intermediate position transverse to the pipeline axis. The slide gate adjustment is effected parallel to the main span of the slide gate housing via a threaded spindle or piston rod, be it manually, by a motor, or the like. In the installed state no leaks must occur at the slide gate, either in the region of the flanges and the plate leadthrough or in the slide gate passage, which is why seals are provided for both directions.
Slide gates are subject to corrosion and wear. The sealing parts and wear parts of the slide gate have to be renewed occasionally if necessary. Further requirements in addition to perfect operation are that the slide gate is cost-effective and simple in its construction, and that the seals and/or the wear parts can be replaced rapidly in an uncomplicated manner.
A large number of different solutions has already been produced in order to comply with all these requirements. Thus it is proposed according to US Pat. No. 4,112,969 that the slide gate housing is composed of two half faces which each incorporate a flange, a yoke for guiding the slide gate plate, and also the slide gate plate and a one-piece liner. The liner forms a sealing stem for the slide gate plate and a flange sealing ring. The sealing liner can be exposed by separating the two half faces and can then be replaced by a new liner, for example. In the region of the flange sealing ring, the half faces surround the sealing liner consisting of plastic in the manner of a ring, wherein the corresponding half faces can simply be slid over the sealing ring. The one-piece sealing liner according to U.S. Pat. No. 4,112,969 has the crucial disadvantage that hardly any sealing function is provided in the slide gate passage due to lack of axial support. Moreover, the liner stem is constructed directly as a sealing element without a separate seal, and is therefore no longer adjustable after installation.
However, parallel-slide gate valves not only have to close in a completely sealed manner, but also have to withstand enormous static and dynamic pressure loadings in very many application situations. U.S. Pat. No. 4,201,365 therefore proposes a somewhat contrasting route. A similarly constructed liner is proposed, with a flange sealing ring and a liner stem. However, the liner stem is provided with a separate slide gate seal. In particular, however, the flange sealing ring is reinforced with two embedded metal supporting rings in order to be able to withstand the corresponding contact load on the slide gate plate at high pressures. The relatively complicated shape of the liner which results from this impedes the simple construction of the slide gate housing in two parts, so that insertion of the liner here, if possible at all, is a very expensive operation; it requires either an extreme resilience for the material of the liner to be extremely resilient or vulcanising-on of the liner, however, so that the latter is no longer replaceable.
The task now set for the invention was to avoid the disadvantages of the known solutions as far as possible. However, ease of installation should be ensured, particularly of the liner also, as well as a complete sealing function.